Multiple cannula image guided tool for image guided procedures

ABSTRACT

Apparatus and methods are disclosed for use within an image-guided surgical navigation system for facilitating the combined positioning and orientation of multiple surgical implements. A tool guide having multiple cannulas is tracked by a surgical navigation system in real time. Position data of the tool guide is registered and combined with pre-acquired images by the navigation computer. Concurrent graphical representations of the plurality of cannulas are superimposed over the images and displayed. The display allows the surgeon to place the tool guide into the patient&#39;s body and position and orient the plurality of cannulas which are then used to place each of the implements.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisionalapplication No. 60/186,200 entitled “Multiple Cannula Image Guided Toolfor Image Guided Procedures,” filed Mar. 1, 2000.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Invention

[0003] The present invention is directed generally to image-guidedmedical procedures, and more particularly, to instrumentation for theoptimal placement of multiple surgical implements using image-basedsurgical guided navigation systems.

[0004] 2. Description of the Related Art

[0005] Many surgical procedures include a surgeon placing multipleimplements within a patient's body. Some of these procedures dictateimplement placement in a specific geometry to maximize the effectivenessof the treatment. Certain factors, such as the characteristics of thepatient's anatomy, can also influence the desired relative placement ofthe multiple implements. Some procedures place the implements at aspecified angle relative to each other, while others may use a parallelarrangement. One such procedure which utilizes a parallel configurationis the fixation of a femoral neck fracture. Typically, this type offracture is stabilized utilizing three parallel cannulated screws. Eachscrew is placed perpendicularly to the fracture site and in such amanner that the distance between each screw is equal, thus forming anequilateral triangle. Parallel placement of the screws is desired sothat the bones are properly pulled together. If the screws are notplaced in such a parallel manner, shearing forces at the fracture sitecan prevent proper healing. Furthermore, the triangular screwarrangement increases the stability of the fracture fixation andprevents rotation between the bone fragments. Studies have suggestedthat three screws are an optimal number since additional implementsprovide no strength advantage and additional screw penetration increasesrisk. Femoral neck fracture stabilization using this method can beperformed percutaneously while the patient is under regional anesthesia,thus reducing risk associated with more invasive procedures.

[0006] Traditional techniques to accurately position and orientimplements have included the use of x-ray images to localize theposition of the implement tool guide. Through the continuous acquisitionof x-ray images during the medical procedure, real-time placement of thetool guide relative to the patient's anatomy can be displayed. Morerecently, fluoroscopically-based surgical navigation systems have beenemployed for tool guide positioning by tracking the tool andsuperimposing its representation onto pre-acquired images withoutrequiring x-rays to be continually taken during the actual surgicalprocedure.

[0007] Current practice for multiple implement placement utilizingimage-based surgical navigation systems typically employs tracked guideswhich contain a single cannula. As used herein, the term cannula refersto a tubular member having at least one hollow channel (i.e., lumen),for insertion in and/or placement adjacent to a patient's body. Such aninstrument could be used to place implements in and/or adjacent to apatient by positioning the cannula in the region of interest, and thenplacing the implement in the region by means of the channel. As usedherein, the term implement refers to a surgical tool or device forperforming medical procedures. An implement could be a drill, a guidewire, or implants such as screws, nails, etc.

[0008] Those skilled in the art should recognize that there are manydifferent types of cannulas and many different ways in which cannulascould be used. For example, a cannula could be rigid, semi-rigid, orflexible and could be configured in any number of different forms, suchas a catheter, needle, endoscope, implement inserter, etc.

[0009] Utilizing a single cannula means the surgeon typically willposition each implement individually. The procedure usually starts byattaching a reference tracking frame to the surgical anatomy. X-rayimages are then taken utilizing a fluoroscopic imager which is alsotracked by the navigation system. The surgeon then positions the trackedguide for the first implement with the aid of the navigational systemdisplay. Once the tool guide is properly positioned, the cannula is usedto place the guide wire and subsequent implement into the desiredanatomical site. The next implement is then placed relative to thefirst, and so on. In order for the surgeon to properly place thesubsequent implement relative to the previous, new images are taken withthe previous implement in place.

[0010] One difficulty of the current practice is in achieving relativeaccuracy of the implement placement. To achieve the desired relativeimplement geometry, the surgeon estimates each trajectory individuallybased upon the prior implements. Thus, the relative accuracy is based onthe physician's estimate. Furthermore, each implement may involvegenerating a new set of images of the patient's anatomy before thesubsequent implement can be placed, which can increase the time of theprocedure and radiation exposure to both the patient and operating roompersonnel.

SUMMARY OF THE INVENTION

[0011] The present invention is directed generally to image guidedmedical procedures, and, particularly, medical procedures which utilizesurgical implements. More specifically, the present invention isdirected to an apparatus and method for the combined positioning ofmultiple implements, especially those that may be placed in a specificrelative geometry.

[0012] As embodied and broadly described herein, certain aspects of theinvention are directed to a multiple cannula tool guide for use inconjunction with image-guided surgical navigation systems.

[0013] In one aspect of the invention, an apparatus for use in imageguided surgery is presented. The apparatus comprises: an instrumentlocation system for detecting position, where the instrument locationsystem includes a computer processor; a tool guide comprising aplurality of cannulas; and at least one trackable marker provided on thetool guide for detection by the instrument location system; a memorycoupled to the computer processor stores: at least one pre-acquiredimage of a patient having an image space, and instructions, to beexecuted by the computer processor, to align the image space to adetector space, to track a three-dimensional position of the tool guidein the detector space, and to compute a projection of the tool guideinto the at least one pre-acquired image.

[0014] In another aspect of the invention, an apparatus for theplacement of surgical implements is presented. The apparatus comprises:a plurality of cannulas coupled to a fixture, where at least onetrackable marker associated with the cannulas; a plurality of surgicalimplement receivers provided on the fixture for receiving surgicalimplements; and at least one of the plurality of receivers beingsubstantially coaxially aligned with a respective one of the pluralityof cannulas.

[0015] In another aspect of the invention, an apparatus for theplacement of surgical implements, is presented. The apparatus comprises:a plurality of cannulas, where at least one of the plurality of cannulasis adjustable to vary its length; a fixture coupled to the plurality ofcannulas, where the fixture can accommodate at least one of theplurality of cannulas being individually adjustable to vary at least oneof its angular position; and at least one trackable marker associatedwith the cannulas.

[0016] In another aspect of the invention, a method for guiding amedical instrument for use in image guided surgery is presented. Themethod comprises: providing at least one pre-acquired image of apatient, the at least one image having an image space; aligning theimage space and a detector space; tracking a three-dimensional positionof a tool guide in the detector space, using at least one trackablemarker provided on the tool guide, where the tool guide includes aplurality of cannulas; and relating the position of the cannulas withthe at least one pre-acquired image.

[0017] Combined positioning of surgical implements may mitigate theamount of estimation a surgeon performs when positioning implementsindividually. This can result in improved placement efficiency andreduced surgical procedure time. Additional savings in time may also berealized by reducing the number of pre-acquired images generated duringa surgical procedure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in andconstitute a part of this specification, illustrate several embodimentsof the invention and together with the description, serve to explain theprinciples of the invention.

[0019]FIG. 1 is a simplified block diagram of a system for the combinedpositioning of multiple surgical implements consistent with the presentinvention.

[0020]FIG. 2 is a simplified side view of an embodiment of a system forthe combined positioning of multiple surgical implements consistent withthe present invention.

[0021]FIG. 3 is a perspective view of an embodiment of a tool guideconsistent with the present invention.

[0022]FIG. 4 is a rear view of the embodiment of the tool guide shown inFIG. 2.

[0023]FIG. 4a is a perspective view of another embodiment of a toolguide consistent with the present invention.

[0024]FIG. 4b is another embodiment of the tool guide having the abilityto adjust the relative angles between the cannulas.

[0025]FIG. 5 is a block diagram of a process used to place surgicalimplements consistent with the present invention.

[0026]FIG. 6 is a simplified block diagram of an exemplary computersystem used in the surgical navigation system in accordance with oneembodiment of the invention.

[0027]FIG. 7 is an exemplary diagram of a display consistent with anembodiment of the invention showing the trajectory of cannulassuperimposed on images of a patient's anatomy.

DETAILED DESCRIPTION

[0028] Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

[0029] With reference to FIG. 1, there is shown schematically anapparatus in accordance with the present invention for the combinedpositioning of multiple surgical implements. Image-based surgicalnavigation system 100 enables a surgeon to generate and display onmonitor 115 a plurality of positions representing each cannula 127 oftool guide 125. Data representing one or more pre-acquired images 105 isfed to navigation computer 110. The pre-acquired images, generated priorto implement placement, typically are taken from different orientationsand represent the region of interest of a patient's body which is toreceive the implements. Navigation computer 110 tracks the position oftool guide 125 in real time utilizing a detector. The detector may be ansensor array 120 physically uncoupled from tool guide 125.Alternatively, the detector could also be at least one trackable marker121 physically attached to or integrated into tool guide 125. Computer110 then registers and displays the position of each cannula 127 withimages 105 in real time to allow the surgeon to properly position andorient the tool guide into the anatomy for implement placement. Thepre-acquired images 105 are superimposed on the icons representing eachcannula 127 on monitor 115. While the present invention described inmore detail below is exemplified by a fluoroscopic-based system used forfemoral neck fracture fixation, it is not limited to the describedembodiment.

[0030]FIG. 2 illustrates apparatus 125 in use with a preferredimage-based surgical navigation system 200 according to one embodimentof the present invention. System 200, described below in sufficientdetail to allow an understanding and appreciation of the presentinvention, is explained in greater detail in U.S. patent applicationSer. No. 09/274,972 of David A. Simon et al., entitled “NavigationGuidance via Computer Assisted Fluoroscopic Imaging,” filed on Mar. 23,1999, the entire disclosure of which is hereby incorporated byreference. However, it must be understood that the invention is notconfined to use with this particular image guided surgical system.

[0031] Further referring to FIG. 2, an image-based surgical navigationsystem 200 for acquiring and displaying x-ray images appropriate for agiven surgical implement procedure is shown. Pre-acquired images ofpatient 202 are collected when a patient, lying on platform 205, isplaced within C-arm 212 of imaging device 210. The term “pre-acquired,”as used herein, does not imply any specified time sequence. Pre-acquiredimages could be generated pre-procedurally or intra-procedurally.Preferably, the images are taken before implement positioning isperformed.

[0032] C-arm 212 may be capable of rotating relative to patient 202,allowing images of the patient to be taken from multiple directions. Forexample, the surgeon may rotate C-arm 212 about its mechanical axis asshown by arrows 228. Usually, images are taken from two substantiallyorthogonal directions, such as anterior-posterior (A-P) and lateral, ofthe anatomy which is to receive the surgical implements. Oneimplementation of imaging device 210 is the Model 9600 C-arm fluoroscopefrom OEC Medical Systems, Inc. of Salt Lake City, Utah.

[0033] It is to be understood, however, that the invention is notconfined to the use of a C-arm fluoroscopic device. Other embodiments ofthe invention could include imaging systems which produce 3-D volumetricdata. Examples of such 3-D imaging systems include computer tomography,ultrasound, or magnetic resonance imaging. Functional imaging systemssuch as, for example, functional magnetic resonance imaging, positronemission tomography, single photon emission tomography, ormagnetoencephalography, could also be used.

[0034] Fluoroscopic images taken by imaging system 210 are transmittedto computer 226 where they may be forwarded to surgical navigationcomputer 110. Image transfer may be performed over a standard videoconnection or a digital link. Computer 110 provides the ability todisplay, via monitor 115, as well as save, digitally manipulate, orprint a hard copy of the received images. Images, instead of, or inaddition to, being displayed on monitor 115, may also be displayed tothe surgeon through a heads-up display or some other type of appropriatedisplay device.

[0035] Although computers 226 and 110 are shown as two separatecomputers, they alternatively could be variously implemented as asingle-chassis multi-processor computer or as a single computer thatperforms the functions performed by individual computers 110 and 226. Inthe single computer case, such computer would directly receive imagedata from image device 210 directly and detector 120.

[0036] Further referring to FIG. 2, image-based surgical navigationsystem 100 generally performs the real-time tracking of tool guide 125,and, in the shown embodiment, also tracks the position of C-arm receiversection 216 and anatomical reference frame 260. This embodiment utilizesa detector which includes a sensor array 120 which is suspended by mount250. Sensor array 120 may be located in such a manner as to provide aclear line of sight to the tracking markers on each tracked object (suchas tracking markers 265, described more fully below). Sensor array 120is coupled to computer 110 which may be programmed with software modulesthat analyze the signals transmitted by sensor array 120 to determinethe position of each object in detector space. The manner in which thesensor array localizes the object is known in the art. See also, forexample, PCT Application No. PCT/US95/12894 (Publication No. WO96/11624) to Bucholz, the entire disclosure of which is incorporated byreference.

[0037] The tracking markers for each tracked object may be, for example,reflective markers and/or light emitting diodes (LEDs). Other devicesknown in the art may be used that are capable of being tracked by acorresponding detector within the scope of the invention. For purposesof illustration, and not by limitation, the tracking means may beacoustic, magnetic, optical, electromagnetic, inertial, and radiologicaldevices known in the art. It should also be understood that differenttracking markers for each tracked object can be used.

[0038] Not all of the tracking devices listed above are used inconjunction with sensor array 120. For example, a single electromagnetictracking marker is actually a sensor which may be used to provide atleast three degrees of spatial information in detector space. Someelectromagnetic sensors can also provide additional attitudeinformation, thus providing up to six degrees of positional information.Such sensors may also have no line of sight constraint which providesthe advantage of functioning while embedded within a patient. The mannerin which electromagnetic sensors localize an object is well known in theart. See also, for example, PCT Application No. PCT/GB93/01736(Publication No. WO 94/04938) to Bladen, the entire disclosure of whichis incorporated by reference.

[0039] In the embodiment of FIG. 2, anatomical reference frame 260,which incorporates a plurality of tracking markers 265, is attached topatient 202 during an implement procedure. The reference frame may besecurely attached to the anatomy in the region of the body which is toreceive the implements. Reference frame 260 may be placed in a positionso that the markers are visible to sensor array 120 during the imageacquisition process and the implement procedure. By sensing attachedtracking markers 265, computer 110 can determine the position of theanatomy in detector space. This information is later used by computer110 to register pixels found in the images to the position of thepatient's anatomy as described in detector space. For purposes of thisdocument, detector space is defined herein as the three-dimensionalreference coordinate system associated with the detector.

[0040] Further referring to FIG. 2, multiple cannula tool guide 125 maybe tracked by surgical navigation system 100 using attached trackingmarkers 230 in order for its position to be determined in detectorspace. Computer 110 integrates this information with the pre-acquiredimages of patient 202 to produce a display which assists surgeon 270when performing multiple implement procedures. Representations ofmultiple cannulas 127 are overlaid on the pre-acquired images of patient202 and displayed on monitor 115. In this manner, surgeon 270 is able tosee the location of the cannulas relative to the patient's anatomy, andcan position and orient multiple implements into the desired portion ofpatient's body.

[0041] Image-based surgical navigation system 100 utilized in theembodiment of the invention shown in FIG. 2 may be the same as that usedin the FluoroNav™ system, which utilizes the StealthStation® TreatmentGuidance Platform, both of which are available from Medtronic SofamorDanek, Inc.

[0042]FIG. 3 is a perspective drawing of an embodiment of tool guide 125which is optimized for the combined positioning of cannulated screws tosecure femoral neck fractures. A plurality of tracking markers 230 arepositioned at points on the upper surface of frame 300. Frame 300 firmlyattaches to a body 305 of tool guide 125 by sliding onto a dovetailformed on the top of mounting post 380. Frame 300 may be interchangedwith other frames which utilize different sizes or shapes, or trackingmarkers of a different type. In the embodiment shown in FIG. 3, trackingmarkers 230 may be infrared LEDs and/or reflective markers such as thosesupplied by Northern Digital Inc.

[0043] For the embodiment shown in FIG. 3, tool guide 125 includes threesubstantially parallel cannulas 310 a, 310 b, 310 c. Cannula 310 a has afixed length and the other cannulas 310 b, 310 c have lengths which arevariable. However, in general, the invention could comprise a tool guidewhere all the cannulas, or any subset thereof, may have variablelengths. The variable length cannulas can be independently adjusted bythe use of threaded means 330, which screw into interchangeable fixture350 and are locked in place using a set screw or jam nut (not shown).Variable length cannulas allow tool guide 125 to adapt to the varyingsurface shapes associated with different bone structures. The surgeon,using information from the pre-acquired images, can make the properlength adjustment to each adjustable cannula during the pre-operativeplanning stage of the medical procedure. The cannulas may possess teeth360 a, 360 b, 360 c at their distal end in order to effectively grip thepatient's bone.

[0044] Furthermore, tool guide 125 may have cannulas which have innerand outer diameters that are also variable. These diameters may bealtered by simply interchanging a given cannula with another havingdiffering diameters, or alternatively, using cylindrical adapters tomodify the diameters of an existing cannula. For example, the innerdiameter of the lumen may be reduced by inserting a reduction sleevewhich extends the length of the cannula. Various reductions in lumendiameter can be achieved through the insertion of one or more reductionsleeves. Alternatively, the outer diameter of a cannula may be increasedin a similar manner by sliding one or more expansion sleeves over theoutside of the cannula. Other embodiments of tool guides can be providedby changing fixture 350. For example, one such interchangeable fixture350 could have cannulas with non-parallel, fixed angular offsets. In theembodiment of FIG. 3, cannulas 310 b and 310 c can be removed byunscrewing them from fixture 350. The fixture may then be slid offcannula 310 a and replaced with another having differentcharacteristics. For example, the number of cannulas can be varied byutilizing fixtures which have a different number of attachment points.Additionally, the relative geometry, or spread, between the cannulas canbe varied by utilizing fixtures which have attachment points indifferent relative locations. Finally, the relative angulations amongthe cannulas may be altered from a parallel configuration by employing afixture having attachment points with fixed angular offsets.

[0045] Many different types of cannulas could be used with the inventionin its broadest aspects. In the embodiment shown in FIG. 3, the cannulas360 a, 360 b, 360 c are preferably substantially rigid tubular memberseach having a lumen extending therethrough that is configured to allowfor passage of surgical implements, such as drills or other tools,and/or devices, such as cannulated screws, nails, etc.

[0046] The surgeon typically holds and manipulates tool guide 125 bygrasping handle 340 shown in FIG. 3. Alternatively, the invention couldalso be physically manipulated by a machine, such as, for example, arobotic arm. Machine manipulation could be facilitated through acoupling on body 305 which could allow tool guide 125 to be removablyattached to a mechanized placement system. This arrangement couldfacilitate highly accurate placement of surgical implements, withoutusage of handle 340.

[0047]FIG. 4 is a rear-view perspective drawing of the embodiment oftool guide 125 shown in FIG. 3. Situated towards the proximal end of theeach cannula is a flange 370, attached to body 305. At the flange centeris a countersunk hole 375 which leads to the lumen of the cannula.Flange 370 and hole 375 is a surgical implement receiver which assiststhe surgeon in the placement of implements down the cannulas once toolguide 125 is properly positioned in the patient's body. For a procedure,for example, to secure a femoral neck fracture, a drill with an attachedguide wire is sequentially placed down each cannula after tool guide 125has been appropriately positioned relative to the patient's body. Thesurgeon drills into the bone in order to anchor the guide wire. Acannulated screw is then placed over each guide wire and the screw istapped into the bone at the fracture site. Once the screws are in placeand secured, the guide wires are removed along with tool guide 125.

[0048]FIG. 4a shows an embodiment of a tool guide having electromagneticsensors attached to cannulas 310 a, 310 b, and 310 c. Electromagneticsensors may be placed at the approximate mid-point of each cannula, asshown by 315 a, 315 b, and 315 c, and/or they may be placed towards thetips of each cannula as shown by 317 a, 317 b, and 317 c.Electromagnetic sensor groups 315 a-c and 317 a-c may be used separatelyor in conjunction with each other. Utilizing both groups can allow forthe extraction of trajectory information of each cannula. Typically,each cannula would be equipped with separate electromagnetic sensors,however; some embodiments may have just one, or any subset of the totalnumber of cannulas, equipped with electromagnetic sensors.

[0049]FIG. 4b exemplifies another embodiment of a tool guide havingcannulas with adjustable relative angles. Cannulas 401 and 402 are setin fixture 405 such that the base of each cannula can pivot within thefixture. The angle of each cannula can be varied independently in theazimuth, θ, 412 and elevation, φ, 414 directions relative to fixture405. After the angles for each cannula have been adjusted as desired,mechanism 410 can lock each cannula in place. Mechanism 410 can be afriction or compression lock, or any other type of locking mechanismknown in the art. The orientation of cannulas 401, 402 shown as mutuallyparallel in FIG. 4b is only for purposes of explanation, and notlimitation. Other embodiments which allow the cannulas to have a varyingangular position which are known in the art could be used. It shouldalso be understood that the tool guide shown in FIG. 4b could have anynumber of cannulas, and in addition to each angle being variable, eachcannula could be individually adjusted in length.

[0050]FIG. 5 is a flowchart illustrating methods for multiple implementpositioning using image-based surgical navigation techniques. Thesurgeon may begin by acquiring one or more images of a patient. In oneembodiment, these may be acquired with fluoroscopic x-ray imager 210, asshown in system of FIG. 2. Alternatively, such images may be acquiredwith an imaging device with provides 3-D volumetric data (step 510).

[0051] Computer 110 then retrieves a pre-acquired image and correlatesthe spatial coordinates defined by the images, known as image space,with the spatial coordinates defined by the detector, known as detectorspace. As shown in the embodiment of FIG. 2, computer 110 may retrieve apre-acquired image from C-arm control computer 226. Computer 110 thendetermines location information of receiver section 216, and anatomicalreference frame markers 265, using sensor array 120. Computer 110 thencorrelates the images to anatomical reference marker 260, by determiningand applying a geometric transform well known to those skilled in theart. Computer 110 then stores the image along with its positionalinformation (step 520). The processes described in step 520 are repeatedfor each image to be acquired.

[0052] The implement placement procedure starts once a detector andcomputer 110 detect and track the position of tool guide 125 relative topatient 202 in detector space. With this information, computer 110dynamically calculates, in real time, the projections of cannulas 127into each image as tool guide 125 is moved by surgeon 270. Typically,the surgeon places the cannulas into the patient percutaneously into theregion of interest to position the implements (step 530). However, theinvention can be used with other surgical techniques.

[0053] Graphical representations of cannulas are superimposed onpre-acquired images and displayed on monitor 115. The cannulas can bedisplayed, simultaneously if desired, and in real time relative to thepatient's anatomy (step 540). The surgeon, utilizing the display, canthen manipulate tool guide 125 and position cannulas 127 in the regionof interest. Using real-time display 115, the physician gets feedback onhow the cannulas are oriented relative to the anatomy and thendetermines the optimal orientation (step 550). Once this is determined,the surgeon will then sequentially place the implements into thepatient. If, for example, the procedure involves the fixation of afemoral neck fracture as previously described, the surgeon first placesa drill with an attached guide wire down the cannula to drill into thebone at the fracture site and then anchor the guide wire into the bone.The surgeon then places a cannulated screw over the guide wire and downinto the cannula. The screw taps into the bone at the fracture site andpulls the separate pieces of bone together. This process is repeated foreach cannulated screw while the surgeon steadily holds tool guide 125 inplace. Alternatively, the surgeon may place the guide wires using thecannulas and then remove the guide from patient's body. The surgeonwould then position the screws by placing them over each guide wire,leading them to the bone into the fracture site (step 560).

[0054] Referring to FIG. 6, components and modules of a computer system110 used to perform various processes of the present invention aredescribed. Although a STEALTH STATION® image guided system manufacturedby Medtronic Sofamor Danek has been identified, it will be appreciatedthat the present invention may be utilized with other types of computersystems. One aspect of the computer system 110 includes a graphical userinterface system operating in conjunction with a display screen of adisplay monitor 115. The graphical user interface system is preferablyimplemented in conjunction with operating system 615 running computer110 for displaying and managing the display objects of the system. Thegraphical user interface is implemented as part of the computer system110 to receive input data and commands from a conventional keyboard 620and mouse 625. For simplicity of the drawings and explanation, manycomponents of a conventional computer system have not been illustratedsuch as address buffers, memory buffers, and other standard controlcircuits because these elements are well known in the art and a detaileddescription thereof is not necessary for understanding the presentinvention. A computer program used to implement the various steps of thepresent invention is generally located in memory unit 600, and theprocesses of the present invention are carried out through the use of acentral processing unit (CPU) 605. Those skilled in the art willappreciate that the memory unit 600 is representative of both read-onlymemory and random access memory. The memory unit also includes adatabase 650 that stores data, for example, image data and tables,including such information as position data and geometric transformparameters, used in conjunction with the present invention. CPU 605, incombination with the computer software comprising operating system 615,detection software module 630, tracking software module 635, calibrationsoftware module 640, and display software module 645, controls theoperations and processes of computer system 110. The processesimplemented by CPU 605 may be communicated as electrical signals alongbus 660 to an I/O interface 670 and a video interface 675.

[0055] Detection software module 630 utilizes signals from the detectorand performs the processes associated with creating a coordinatereference system and detecting positions of reference images for use inconnection with the present invention and are known to those skilled inthe art. Tracking software module 635 performs the processes necessaryfor tracking objects in an image guided system as described herein andare known to those skilled in the art. Correlation software module 640computes the geometric transform which registers the images to thedetector space, and thus the patient's anatomy.

[0056] Display software module 645 applies, and if necessary, computesthe offsets between tool guide tracking markers 230 and the cannulas inorder generate an icon representing each cannula for superposition overthe images. For tool guides with fixed cannulas, these offsets can bemeasured once and stored in database 650. The user would then selectfrom a list of tool guides which one was being used in the procedure sothe proper offsets are applied by display software module 645. For toolguides with variable lengths and angulations, the offsets could bemeasured manually and entered via keyboard 620, or measured using thenavigation system 100 in conjunction a tracked pointer or trackedregistration jig (not shown). If a tracked pointer is used, the userwill touch the tip and tail of each cannula while the tool guide isbeing tracked. The offsets are computed by display software module 645and stored for later use. Similarly, if a tracked registration jig isused, the tool guide is placed within the jig while it is being tracked.The jig will measure the positions of the cannulas and display softwaremodule 645 will again compute the offsets and store them for later usein database 650.

[0057] Pre-acquired image data 105 can be fed directly into computer 110digitally through I/O interface 670, or may be supplied as video datathrough video interface 675. In addition, items shown as stored inmemory can also be stored, at least partially, on hard disk 680 ifmemory resources are limited. Furthermore, while not explicitly shown,image data may also be supplied over a network, through a mass storagedevice such as a hard drive, optical disks, tape drives, or any othertype of data transfer and storage devices which are known in the art.

[0058]FIG. 7 shows an exemplary diagram of display 700 illustrating aniconic graphical overlay of the cannulas for the preferred embodiment.Display 700 is presented to the surgeon on monitor 115 of computersystem 110. The left side of FIG. 7 shows a fluoroscopic image of ananterior-posterior view of a hip and femoral neck bone 710. Graphicaloverlays 715 are the iconic superposition of all the cannulas 127attached to tool guide 125 within image 710. Graphical overlays 715 aredirectional indicators, displaying the position and orientation of eachcannula. In the embodiment shown in FIG. 7, these directional indicatorsare shown as lines, but other symbols may be used. As the surgeon movestool guide 125, computer 110 recalculates and displays the new locationsof the graphical overlays 715. The surgeon can use image 710 andoverlays 715 to visualize, in real-time, the position and orientation ofthe cannulas relative to the patient's anatomy.

[0059] For the embodiment shown in FIG. 2, the surgeon would like toacquire two substantially orthogonal fluoroscopic images of patient 202,such as images from an anterior-posterior view and a lateral view of theanatomy of interest. These two complementary views help the surgeon tobetter visualize how the cannulas are situated in the patient's anatomy.The orthogonal views are related to one another by a 90 degree rotationabout the major axis of the patient (the axis running along the lengthof the patients body). The fluoroscopic image taken from the lateralview 720 is shown on the right side of FIG. 7, along with graphicaloverlays 717 showing the locations of the cannulas 127.

[0060] In certain situations, the surgeon may wish to know where the tipof the cannulas would be if cannulas were projected along a line give bya tool guide's current trajectory. At the surgeon's command, computer110 may calculate and display this projection based upon the currentorientation and position of the cannulas. This orientation and positionare determined by tracking the tip and the tail of each cannula. Theestimated position of the tip can be calculated by computer 110 throughprojecting a fixed distance beyond the cannulas' tips in the directionof the line formed by each cannula's tip and tail. The estimatedposition, or “look-ahead” trajectory, would be represented by agraphical overlay. As shown in FIG. 7, exemplary “look-ahead”trajectories 725 and 727 are shown in a different line styles fromoverlay 715 and 717, respectively. This difference could also be achange in color, type, or texture between the look-ahead trajectory 725,727 and the current position 715, 717. Computer 110 may vary the lengthof the look-ahead trajectory 725, 727 as directed by the surgeon throughthe graphical user interface control 730 and computer keyboard 620 ormouse 625. In this manner, computer 110 assists the surgeon invisualizing where the cannulas would be in the patient if they wereadvanced a predetermined distance into the body of the patient.

[0061] Although the look-ahead technique described above projected thegraphical representation of the cannulas into the image, there is norequirement that the cannulas' graphical representation be in the spaceof the image for look ahead trajectory 725, 727 to be projected into theimage. In other words, for example, the surgeon may be holding toolguide 125 above the patient and outside the space of the image, so thatthe representation of the cannulas does not appear in the images.However, it may still be desirable to project ahead portion 725, 727into the image to facilitate planning of the implement procedure.

[0062] The look-ahead technique could be extended to include virtualimplants. Graphical overlays representing implant structures such asprosthetic devices, plates, and fasteners such as screws, nails, etc.,could be shown on display 115 during and after their placement into thepatient's body. These graphical overlays would provide additionalinformation regarding the implants without involving the generation ofnew images.

[0063] When cannulas 127 are perpendicular to the plane of thefluoroscopic image, the graphical overlay of the cannulas may virtuallycollapse to a point, potentially making it difficult to view them. Toalleviate this, computer 110 may optionally use a different graphicalrepresentation of cannulas 172 when the distance in the image planebetween the tip and tail of the cannulas 127 becomes smaller than somefixed distance.

[0064] The foregoing description is presented for purposes ofillustration and explanation. It is not intended to be exhaustive or tolimit the invention to the precise form disclosed, and modifications ofvariations are possible in light of the above teachings or may beacquired from practice of the invention. The principles of the inventionand its practical application enable one skilled in the art to utilizethe invention in various embodiments and with various modifications asare suited to the particular use contemplated.

[0065] For example, pre-acquired images obtained from modalitiesdifferent than the C-arm fluoroscope x-ray imager may be used with theinvention. Such modalities could supply 3-D volumetric data and may alsoinclude functional information. Such modalities may include, by way ofexample only, computer tomography, ultrasound, or magnetic resonanceimaging. Imaging modalities which may provide functional informationinclude functional magnetic resonance imaging, positron emissiontomography, single photon emission tomography, magnetoencephalography,or any other modality known to those skilled in the art.

[0066] Furthermore, the invention is not limited to the fixture offemoral neck fractures, but can be used for many different types ofprocedures such as the distal locking of intramedullary nails, inplacing implements such as interbody fusion devices into the spine,anterior cervical plating systems, etc., or any other application wheretwo or more implements are to be placed, especially multiple implementshaving fixed relative positions and angulations.

What is claimed:
 1. An apparatus for use in image guided surgery,comprising: an instrument location system for detecting position, theinstrument location system including a computer processor; a tool guidecomprising: a plurality of cannulas, and at least one trackable markerprovided on the tool guide for detection by the instrument locationsystem; and a memory coupled to the computer processor, storing: atleast one pre-acquired image of a patient, the at least one pre-acquiredimage having an image space, and instructions, to be executed by thecomputer processor, to align the image space to a detector space, totrack a three-dimensional position of the tool guide in the detectorspace, and to compute a projection of the tool guide into the at leastone pre-acquired image.
 2. The apparatus of claim 1, further comprising:a frame associated with the plurality of cannulas, wherein the at leastone trackable marker is provided on the frame for detection by theinstrument location system.
 3. The apparatus of claim 1, wherein the atleast one trackable marker is associated with the plurality of cannulas.4. The apparatus of claim 1, further comprising: a display operablyconnected to the computer processor; and additional instructions storedin the memory, to be executed by the computer processor, to display theat least one pre-acquired image, and to superimpose a first set ofsymbols on the at least one pre-acquired image, the first set of symbolsrepresenting current positions of the plurality of cannulas with respectto the patient.
 5. The apparatus of claim 2, further comprising: acentral structure coupled to the plurality of cannulas and to the frame;and a handle coupled to the central structure, wherein the handle isused for manually manipulating the tool guide.
 6. The apparatus of claim3, further comprising: a handle coupled to the tool guide, wherein thehandle is used for manually manipulating the tool guide.
 7. Theapparatus of claim 1, wherein the tool guide is coupled to machineoperated means for manipulating the tool guide.
 8. The apparatus ofclaim 1, wherein at least one of the plurality of cannulas isindividually adjustable in at least one of length and angular position.9. The apparatus of claim 1, wherein at least one of the plurality ofcannulas is individually adjustable in at least one of inner diameterand outer diameter.
 10. The apparatus of claim 5, wherein the centralstructure is removably coupled to the frame.
 11. The apparatus of claim1, further comprising: an interchangeable fixture coupled to theplurality of cannulas, wherein the interchangeable fixture is used foraccommodating at least one of: a variable number of cannulas, cannulashaving a plurality of relative placements, and cannulas having aplurality of fixed relative angles.
 12. The apparatus of claim 4,wherein the first set of symbols are a plurality of directionalindicators, each of the indicators illustrating one of the plurality ofcannulas.
 13. The apparatus of claim 4, further comprising: additionalinstructions stored in the memory, to be executed by the computerprocessor, to compute a predicted path of the plurality of cannulasbased on their current location and orientation, and to superimpose asecond set of symbols on the at least one pre-acquired image, the secondset of symbols representing predicted positions of the plurality ofcannulas with respect to the patient.
 14. The apparatus of claim 4,further comprising: additional instructions stored in the memory, to beexecuted by the computer processor, to superimpose a third set ofsymbols representing at least one surgical implement.
 15. The apparatusof claim 13, wherein the second set of symbols are a plurality ofdirectional indicators having at least one of a color, style, shape,size and texture differing from that of the first set of symbols fordifferentiating the predicted positions from the current positions. 16.The apparatus of claim 1, further comprising: a reference frameattachable to the patient, the reference frame having at least onetrackable marker for detection by the instrument location system. 17.The apparatus of claim 1, wherein the at least one pre-acquired image isgenerated using a C-arm fluoroscope.
 18. The apparatus of claim 1,wherein the at least one pre-acquired image is generated using an imagerwhich produces three-dimensional volumetric data, the imager includingone of a computer aided tomography system, a magnetic resonance imagingsystem, a positron emission tomography system, and an ultrasound imagingsystem.
 19. The apparatus of claim 1, further comprising: a functionalimaging system including one of a functional magnetic resonance imagingsystem, a positron emission tomography system, a single photon emissiontomography system, and a magnetoencephalography system.
 20. Theapparatus of claim 4, wherein the at least one pre-acquired imageincludes a plurality of images taken from different orientations anddisplayed on the display.
 21. The apparatus of claim 20, wherein thedifferent orientations are generally orthogonal.
 22. An apparatus forthe placement of surgical implements, comprising: a plurality ofcannulas coupled to a fixture; at least one trackable marker associatedwith the plurality of cannulas; and a plurality of surgical implementreceivers provided on the fixture for receiving surgical implements, atleast one of the plurality of receivers being substantially coaxiallyaligned with a respective one of the plurality of cannulas.
 23. Theapparatus of claim 22, further comprising: at least one trackable markerprovided on a frame, the frame being associated with the plurality ofcannulas, wherein the at least one marker being arranged for detectionby an instrument location system.
 24. The apparatus of claim 22, furthercomprising: a peripheral structure, coupled to the fixture, formaneuvering the cannulas during a surgical procedure to place thesurgical implements.
 25. The apparatus of claim 22, wherein at least oneof the surgical receivers is a flange configured to receive the surgicalimplements.
 26. The apparatus of claim 22, wherein at least one of theplurality of cannulas is individually adjustable to vary its length. 27.The apparatus of claim 22, wherein at least one of the plurality ofcannulas is individually adjustable to vary at least one of its angularpositions.
 28. The apparatus of claim 27, wherein the at least oneangular position is an azimuth angular position measured in a horizontalreference plane associated with the fixture.
 29. The apparatus of claim27, wherein the at least one angular position is an elevation angularposition measured in a vertical reference plane associated with thefixture.
 30. The apparatus of claim 22, wherein the fixture isinterchangeable and is configured to accommodate at least one of: avariable number of cannulas, cannulas having a plurality of relativeplacements, and cannulas having a plurality of fixed relative angles.31. The apparatus of claim 24, wherein the peripheral structure is ahandle.
 32. The apparatus of claim 24, wherein the peripheral structureis machine operated means.
 33. The apparatus of claim 23, furthercomprising: a plurality of interchangeable frames, at least two of theframes having a different type of trackable marker.
 34. The apparatus ofclaim 22, wherein the surgical implement is at least one of a surgicaltool and an implant.
 35. The apparatus of claim 22, wherein at least oneof the plurality of cannulas can be interchanged with a cannula havingat least one of a different inner diameter and outer diameter.
 36. Theapparatus of claim 22, wherein at least one of the plurality of cannulasis individually adjustable to vary at least one of its inner diameterand outer diameter.
 37. The apparatus of claim 22, wherein at least oneof the plurality of cannulas includes a serrated structure for grippingportions of a patient's anatomy.
 38. An apparatus for the placement ofsurgical implements, comprising: a plurality of cannulas, wherein atleast one of the plurality of cannulas is adjustable to vary its length;a fixture coupled to the plurality of cannulas, wherein the fixture canaccommodate at least one of the plurality of cannulas being individuallyadjustable to vary at least one of its angular position; and at leastone trackable marker associated with the cannulas.
 39. The apparatus ofclaim 38, further comprising: at least one trackable marker provided ona frame associated with the cannulas, the markers being arranged fordetection by an instrument location system.
 40. The apparatus of claim38, further comprising: a peripheral structure, coupled to the fixture,for maneuvering the cannulas during a surgical procedure to place thesurgical implements.
 41. The apparatus of claim 38, wherein the at leastone angular position is an azimuth angular position measured in ahorizontal reference plane associated with the fixture.
 42. Theapparatus of claim 38, wherein the at least one angular position is anelevation angular position measured in a vertical reference planeassociated with the fixture.
 43. The apparatus of claim 38, wherein thefixture is interchangeable and is configured to accommodate at least oneof: a variable number of cannulas, cannulas having a plurality ofrelative placements, and cannulas having a plurality of fixed relativeangles.
 44. The apparatus of claim 40, wherein the peripheral structureis a handle.
 45. The apparatus of claim 40, wherein the peripheralstructure is machine operated means.
 46. The apparatus of claim 39,further comprising: a plurality of interchangeable frames, at least twoof the frames having a different type of trackable marker.
 47. Theapparatus of claim 38, wherein the surgical implement is at least one ofa surgical tool and an implant.
 48. The apparatus of claim 38, whereinat least one of the cannulas includes a serrated structure for grippingportions of a patient's anatomy.
 49. The apparatus of claim 39, whereinat least one of the plurality of cannulas is individually adjustable tovary at least one of its inner diameter and outer diameter.
 50. A methodfor guiding a medical instrument for use in image guided surgery,comprising: providing at least one pre-acquired image of a patient, theat least one pre-acquired image having an image space; aligning theimage space and a detector space; tracking a three-dimensional positionof a tool guide in the detector space, using at least one trackablemarker provided on the tool guide, wherein the tool guide includes aplurality of cannulas; and relating positions of the plurality ofcannulas with the at least one pre-acquired image.
 51. The method ofclaim 50, further comprising: computing a projection of at least one ofthe plurality of cannulas into the at least one pre-acquired image;displaying the at least one pre-acquired image on a display; andsuperimposing a representation of the projection on the at least onedisplayed pre-acquired image.
 52. The method of claim 51, wherein therepresentation includes a first set of directional indicators whichrepresent current positions of the plurality of cannulas with respect tothe patient.
 53. The method of claim 51, wherein at least two differentpre-acquired images taken from different orientations are displayed onthe display.
 54. The method of claim 53, wherein the orientations aresubstantially mutually perpendicular.
 55. The method of claim 52,further comprising: computing a predicted path for the plurality ofcannulas based on their current location and orientation; andsuperimposing a second set of directional indicators on the at least onepre-acquired image, the second set of directional indicatorsrepresenting predicted positions of the plurality of cannulas withrespect to the patient.
 56. The method of claim 55, wherein the secondset of directional indicators have at least one of a color, style,shape, size, and texture differing from that of the first set ofdirectional indicators for differentiating the predicted positions fromthe current positions.
 57. The method of claim 50, further comprising:generating the at least one pre-acquired image using a C-armfluoroscope.
 58. The method of claim 50 further comprising: generatingthe at least one pre-acquired image using a three-dimensional volumetricimager, wherein the volumetric imager includes one of a computer aidedtomography system, a magnetic resonance imaging system, a positronemission tomography system, and an ultrasound imaging system.
 59. Themethod of claim 50, further comprising: generating the at least onepre-acquired image using a functional imaging system, wherein thefunctional imaging system includes one of a functional magneticresonance imaging system, a positron emission tomography system, singlephoton emission tomography system, and a magnetoencephalography system.60. The method of claim 50, wherein at least one of the plurality ofcannulas is independently adjustable in at least one of length andangular position.
 61. A system for use in image guided surgery,comprising: means for providing at least one pre-acquired image of apatient, the at least one pre-acquired image having an image space;means for aligning the image space and a detector space; means fortracking a three-dimensional position of a tool guide in the detectorspace, using at least one trackable marker provided on the tool guide,wherein the tool guide includes a plurality of cannulas; and means forrelating positions of the plurality of cannulas with the at least onepre-acquired image.
 62. The system of claim 61, further comprising:means for computing a projection of at least one of the plurality ofcannulas into the at least one pre-acquired image; display means fordisplaying the at least one pre-acquired image; and means forsuperimposing a representation of the projection on the at least onedisplayed pre-acquired image.
 63. The system of claim 62, wherein therepresentation includes a first set of directional indicators whichrepresent current positions of the plurality of cannulas with respect tothe patient.
 64. The system of claim 62, wherein at least two differentpre-acquired images taken from different orientations are displayed onthe display.
 65. The system of claim 64, wherein the orientations aresubstantially mutually perpendicular.
 66. The system of claim 63,further comprising: means for computing a predicted path of theplurality of cannulas based on their current location and orientation;and means for superimposing a second set of directional indicators onthe at least one pre-acquired image, the second set of directionalindicators representing predicted positions of the plurality of cannulaswith respect to the patient.
 67. The system of claim 66, wherein thesecond set of directional indicators have at least one of a color,style, shape, size, and texture differing from that of the first set ofdirectional indicators for differentiating the predicted positions fromthe current positions.
 68. The system of claim 61, further comprising:C-arm fluoroscope means for generating the pre-acquired images.
 69. Thesystem of claim 61 further comprising: means for generating the at leastone pre-acquired image using three-dimensional volumetric imaging means,wherein the three-dimensional volumetric imaging means includes one ofcomputer aided tomography means, magnetic resonance imaging means,positron emission tomography means, and ultrasound imaging means. 70.The system of claim 61, further comprising: means for generating the atleast one pre-acquired image using functional imaging means, wherein thefunctional imaging means includes one of functional magnetic resonanceimaging means, positron emission tomography means, single photonemission tomography means, and magnetoencephalography means.
 71. Thesystem of claim 61, further comprising: means for independentlyadjusting the length of at least one of the plurality of cannulas. 72.The system of claim 61, further comprising: means for independentlyadjusting at least one angular position of at least one of the pluralityof cannulas.
 73. An apparatus for use in image guided surgery,comprising: an instrument location system for detecting position, theinstrument location system including a computer processor; a referenceframe attachable to a patient, the reference frame having at least onereference frame trackable marker for detection by the instrumentlocation system; a tool guide comprising: a plurality of cannulascoupled to a fixture, wherein at least one of the plurality of cannulasis individually adjustable in at least one of length, angular position,inner diameter, and outer diameter; at least one trackable markerprovided on the tool guide associated with the plurality of cannulas; aplurality of surgical implement receivers provided on the fixture, forreceiving surgical implements, at least one of the plurality ofreceivers being substantially coaxially aligned with a respective one ofthe plurality of cannulas, and a handle for manipulating the tool guide;a display operably connected to the computer processor; and a memorycoupled to the computer processor, storing: at least one pre-acquiredimage of a patient, the at least one pre-acquired image having anassociated image space, and instructions that, when executed by thecomputer processor, align the image space to a detector space, track athree-dimensional position of the tool guide in the detector space,compute a projection of at least one of the plurality of cannulas intothe at least one pre-acquired image, display the at least one ofpre-acquired image, superimpose a first set of directional indicators onthe at least one pre-acquired image, wherein the directional indicatorsrepresent current positions of the plurality of cannulas with respect tothe patient, compute a predicted path of each of the plurality ofcannulas based on their current location and orientation, andsuperimpose a second set of directional indicators on the at least onepre-acquired image, the second set of directional indicatorsrepresenting predicted positions of the plurality of cannulas withrespect to the patient, the second set of directional indicators havingat least one of a color, style, shape, size, and texture differing fromthat of the first set of directional indicators for differentiating thepredicted positions from the current positions.
 74. The apparatus ofclaim 73, further comprising: a frame associated with the plurality ofcannulas, wherein the at least one trackable marker is provided on theframe for detection by the instrument location system.
 75. The apparatusof claim 73, further comprising the at least one trackable markerassociated with the plurality of cannulas.
 76. The apparatus in claim73, wherein the at least one pre-acquired image is generated using aC-arm fluoroscope.
 77. The apparatus of claim 73, wherein the at leastone pre-acquired image is generated using an imager which producesthree-dimensional volumetric data, the imager including one of acomputer aided tomography system, a magnetic resonance imaging system, apositron emission tomography system, and an ultrasound imaging system.78. The apparatus of claim 73, further comprising: a functional imagingsystem including one of a functional magnetic resonance imaging system,a positron emission tomography system, single photon emission tomographysystem, and a magnetoencephalography system.
 79. The apparatus of claim73, wherein the fixture can accommodate at least one of: a variablenumber of cannulas, cannulas having a plurality of a relativeplacements, and cannulas having a plurality of fixed relative angles.80. A method for placing implements into a patient during an imageguided medical procedure, comprising: providing at least onepre-acquired image of a patient, the at least one pre-acquired imagehaving an image space; aligning the image space and a detector space;tracking a three-dimensional position of a tool guide in the detectorspace, using at least one trackable marker provided on the tool guide,wherein the tool guide includes a plurality of cannulas; computing aprojection of at least one of the plurality of cannulas into the atleast one pre-acquired image; computing a predicted path of each of theplurality of cannulas based on their current location and orientation;displaying the at least one pre-acquired image on a display;superimposing on the at least one pre-acquired image a first set ofdirectional indicators representing current positions of the pluralityof cannulas with respect to the patient; superimposing on the at leastone pre-acquired image a second set of directional indicators, thesecond set of directional indicators representing predicted positions ofthe plurality of cannulas with respect to the patient; superimposing onthe at least one pre-acquired image a third set of indicators, the thirdset of indicators representing implant structures, including at leastone of a prosthetic device, plates, and fasteners; placing the pluralityof cannulas at a location in a patient's body; orienting the pluralityof cannulas; and utilizing the plurality of cannulas to place implementsin the patient at the location.
 81. The method of claim 80, wherein thesecond set of directional indicators have at least one of a color,style, shape, size and texture differing from that of the first set ofdirectional indicators for differentiating the predicted positions fromthe current positions.
 82. The method of claim 80, wherein the at leastone pre-acquired image is generated using a C-arm fluoroscope.
 83. Themethod of claim 80 further comprising: generating the at least onepre-acquired image using a three-dimensional volumetric imager, whereinthe volumetric imager includes one of a computer aided tomographysystem, a magnetic resonance imaging system, a positron emissiontomography system, and an ultrasound imaging system.
 84. The method ofclaim 80, further comprising: generating the at least one pre-acquiredimage using a functional imaging system including one of a functionalmagnetic resonance imaging system, a positron emission tomographysystem, single photon emission tomography system, and amagnetoencephalography system.